1. Field of the Invention
This invention pertains generally to shielding for radioactive materials and more particularly to a lightweight storage container for radioactive materials.
2. Description of the Background Art
At the present time, there are approximately 560,000 tons of depleted uranium hexaflouride under storage in 50,000 cylinders which cost about $10,000,000 annually to maintain. Putting the depleted uranium to practical use would cut the maintenance costs significantly. One such use of depleted uranium is as shielding material for radioactive materials. Using the depleted uranium in such a manner is not only useful, but also serves to eliminate the depleted uranium from the environment.
The storage and/or transportation of radioactive materials require effective shielding to protect the operating personnel and the surrounding environment. The storage and/or transportation of radioactive materials have been accomplished using canisters, containers, receptacles or vessels that possess photon and neutron absorption capability and sufficient structural strength. The radiation absorption capability shields the environment and operating personnel from radiation emitted by the radioactive materials, while structural strength allows the vessel to withstand normal handling and storage stresses and even some accidental impacts upon the vessel.
One such known storage vessel utilizes a hollow body having lateral walls and a base formed unitarily with one another and open at an upper end. The walls of the body have an outer layer, an intermediate layer and an inner layer. The outer and intermediate layers are cast unitarily from a carbon containing ferrous metal of copper alloy while the intermediate layer consists of a cast matrix phase within which heavy metal particles, such as depleted uranium, are embedded to absorb radiation. A plurality of separate channels disposed longitudinally within the outer layer is filled with neutron absorptive material, and a removable cover is fitted over the upper end after the radioactive has been placed therein.
The multi-layer configuration of such storage vessels result in a shielding system that is large dimensionally and in mass, thus limiting the quantity of radioactive material that can be stored, especially when storage area is limited. Without the separate longitudinal channels containing the neutron absorptive material, the vessel would be ineffective, as depleted uranium is useless by itself for neutron absorption. Such a large multi-layer configuration also requires ancillary cooling systems to dissipate heat generated by the enclosed radioactive material.
Accordingly, there is a need for a radiation storage vessel that combines the functions of attenuating photon radiation, neutron absorption and shock mitigation from impact, while minimizing the thickness of the vessel's walls and weight such that the vessel can be more readily transported and a larger quantity of radioactive material can be stored in a given area. The foregoing reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicant's acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these teach or render obvious, singly or when considered in combination, applicant's claimed invention.